I put a newer exhaust manifold in the '63, the kind with the reinforced ribbing. The output flange is threaded instead of using bolts and nuts as in the old style. They 'appear' to be 7/16 course, but a 7/16-14 will only start to thread then stops, (both holes) and a 7/16-20 won't even catch.
Are these holes metric?

TIA!

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They are not metric, no. At least they're not supposed to be; who knows how some idiot in China might have mis-threaded them.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

A 7/16 bolt would have to be an 11 mm............

which I've never heard of.


You could try a M10 x 1.75 which would be about an
25/64 x 14.5

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks guys. If I can't figure this out I'll have to drop some 3/8s through the holes and use nuts on the ends. I prefer to do things proper, but sometimes we have to improvise.
As far as I know this isn't a Chinese replacement, it looks to be OEM. And I dug around in my spare parts to see if any of the other manifolds I have are threaded. I found one still connected to a super six intake. One of the flange bolts was broken off in the hole, but the other hole was open and it is reacting to the 7/16s bolts the same way as my other manifold. I carefully started a tap in it to see if it was just rust in the threads that was stopping the bolt, but the tap responded the same way, it starts, then stops. If I apply pressure it starts to cut new thread. Very odd....

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I just drill them out oversize and use a stainless bolt and lock nut and nut. They are much easier to remove when time comes to change gaskets. Especially when you step up to a 2.25" head pipe. Assembly goes much quicker.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

When I need new nut for those bolts. I found that 7/16 lug nuts worked quite nicely.